1. Field of the Invention
The present invention relates generally to helmets and more specifically to a helmet having blunt force trauma protection, which includes a replaceable impact layer.
2. Discussion of the Prior Art
The purpose of protective helmets is to prevent head injury incurred during some event, such as football, ice hockey, horseback riding, skiing, lacrosse, baseball, riding a motorcycle, construction and military combat. Helmets were first invented for protection in military engagements, and as such, started as protection from hand held weapons and evolved in the 20th Century to protect from projectiles and explosives. As such, rigid, impenetrable helmets have been the paradigm we have used for the prevention of head injuries.
Rigid helmets have been partially successful at preventing injuries. However, the recent epidemic of concussions and the increasing awareness of the cumulative problems associated with repeated head trauma have unpacked the limitations of the current structure of protective helmets in all sports. Indeed, the same limitation could be claimed for all protective helmets including construction and military helmets.
The physics of head injury is all focused on the distance over which deceleration occurs. The human brain is very fragile, being composed of cells wrapped in membranes made of fluid fatty acids. Several trillion synapses in the brain are delicately poised in proximity to one another, without rigid and strong connections. These synapses are the functional means by which the brain operates. Shaking them disrupts them. The human nervous system has developed a host of strategies to enshrine the delicate neurons and their even more delicate synapse in a protective cocoon of safety. First and foremost, the brain is floating in water (otherwise called the cerebral spinal fluid), creating a bath without rigid inflexible supports. Within that water, the brain is suspended in a delicate spider web of suspending fibers and membranes that keep water from moving too quickly around the surface and allowing the soft brain to be gently suspended within the bony structure of the skull. The skull provides a rigid structure to contain the floating bath of fluid. Of note, the skull can be cracked and shattered as one strategy of dissipating force. This may lead to survival with subsequent healing. It is a unique and delicate bony structure around the brain, not seen anywhere else in the human body. The scalp provides an additional layer of safety. It is mobile and gives when struck, providing a few extra millimeters of deceleration distance. The scalp uniquely tears when stressed by direct blows, creating yet another mechanism of safety. The tearing creates large and dramatic scalp wounds in direct head trauma, but the brain underneath survives. Finally, the human skull is surrounded by hair, which can provide another layer of cushioning.
What are the physics of deceleration injury? The formula is simple: ΔVelocity/time=Deceleration. The change in velocity is divided by time. Rigid structures striking each other have a spike of deceleration within the first 0.00001 seconds. The more rigid and brittle, the higher the G-force generated for a shorter fragment of time. The Holy Grail of injury prevention in deceleration injury is to increase the distance and therefore time during which deceleration occurs. We are familiar with automobiles and have seen the effectiveness of airbags that increase the distance of deceleration of the human torso before it strikes the steering wheel. Vehicles are also designed to crumple so that force is taken up by bending metal, collapsing frames, shattering fenders, stretching seatbelts all of which increase the distance and time over which the human inside decelerates. Each of these strategies also complements the others to have a net effect of human survival, lowing the G forces from sufficient to break bones to simple sprains, strains and bruises.
Protective helmets have, to date, failed to provide a complete cocoon of safety. If the analogy to the human head can be used, protective helmets provide a skull and the inner dura, but there is no outer layer of safety. There is no scalp. No hair. Some advances have been made with the use of external foam with the SG Helmet. The missing ingredient in foam is that it fails to “fail”. The human scalp tears and gives way. Foam doesn't tear. It does provide distance for greater deceleration, resulting in reduction of concussion injuries.
It appears that the prior art does not teach or suggest the use of air bubbles to create a more fluid means of slowing down deceleration and increasing the time/distance over which the deceleration occurs. The value of air bubbles is that they easily deform, have little weight, stretch, deform rapidly with increasing resistance and, in extreme circumstances, burst. Bursting is a critical component, as it allows for the dissipation of force and then allows distance to increase as the next layer of bubbles can absorb the evolving contact. However, the essential stretching and increasing air pressure upon contact makes for a gradient of deceleration, which will provide protection. Foam deforms but is not as fluid as air bubbles, has greater weight, which may result in rotational injuries of the neck. The foam cannot burst thereby dissipating energy.
U.S. Pat. No. 3,872,511 to Nichols discloses protective headgear. U.S. Pat. No. 3,999,220 to Keltner discloses air cushioned protective gear. U.S. Pat. No. 4,586,200 to Poon discloses a protective crash helmet. U.S. Pat. No. 5,129,107 discloses an inflatable safety helmet specially for motorcycling.
Accordingly, there is a clearly felt need in the art for a helmet having blunt force trauma protection, which includes an external replaceable impact layer that covers a rigid helmet and extinguishes an instantaneous G-force deceleration shock wave applied to the rigid helmet.